Remote activity monitoring

ABSTRACT

A method for remotely monitoring activity includes generating first server heartbeat information at a first server at a local site, and storing the first server heartbeat information in a first primary site disk at the local site. The method also includes sending the first server heartbeat information from the first primary site disk, to a first secondary site disk at a remote site. The method further includes receiving information from a second secondary site disk at the local site, and determining if the information received from the second secondary site disk includes updated heartbeat information.

BACKGROUND

1. Technical Field

The present invention relates to remotely monitoring server activity.More particularly, the invention concerns enabling servers at a site todetermine if servers at a remote peer site are operational, even whenprivate and public communication links between the sites are notfunctioning.

2. Description of Related Art

In high performance computing systems, two or more servers (also callednodes) are often connected to form a cluster. During normal operation,at any given time only one server in a cluster can be in control of thecluster, and the server that is in control of the cluster is referred toas “owning” the cluster at that time. Whichever server gains control ofa common resource (for example, a quorum disk) owns the cluster. Anundesirable erroneous condition called “split brain” results if two ormore servers operate as if they have read or write access to the samedata at the same time and believe they each are in control of thecluster at the same time. The split brain condition can result if afirst server erroneously concludes that a second server is notoperational, when the second server is operational. However, the splitbrain condition can be avoided by providing communications between theservers in a cluster. For example, server clustering software may useTCP/IP based communications for transmitting communications, referred toas “heartbeat communications”, between nodes in a cluster fordetermining if all of the nodes are operational. The heartbeatcommunications may be transmitted over a private communications link,which may be a private Ethernet link, between the servers in a cluster.The servers in a cluster may also be connected via a publiccommunications link, which may be an Ethernet link, which is used toconnect one or more client computers that may be running applicationprograms, to the servers. The public Ethernet link may be used as abackup communications link for transmitting heartbeat communicationsbetween the servers in a cluster. If heartbeat communications aredisrupted due to malfunctions of both the private and public Ethernetlinks, a common disk resource may be used to determine which node ownscluster operations in systems in which the servers are not separated bysignificant distances. For example, clustering solutions such asMicrosoft Cluster Server can use a common disk resource, called a quorumdisk, to determine which node owns cluster operations. However, if theservers are separated by significant distances, for example several ortens or hundreds of kilometers, there is no common disk resource, andthere is no way to determine which node owns cluster operations if boththe private and public Ethernet links fail.

As an example, there is no common disk resource when data is mirroredfrom a primary site to a remote secondary site. Many computer users, forexample businesses and governments, update and store data at a primarysite, and maintain a backup copy of the data at a secondary site that isphysically remote from the primary site, which can be used for recoveryfrom a disaster at the primary site. Making a backup copy of data at aremote secondary site is referred to as data mirroring, data shadowing,data duplexing, or remote copying. The servers at the primary site maybe separated from the servers at the secondary site by significantdistances, for example hundreds of kilometers. The InternationalBusiness Machines (IBM) Peer-to-Peer Remote Copy (PPRC) facility is anexample of a widely used synchronous remote data mirroring system.

The significant distance between remote data mirroring sites makes itunlikely that a secondary site will be harmed if there is an equipmentfailure or other disaster that damages or destroys data at the primarysite, thereby permitting data to be recovered from the secondary site inthe event of an equipment failure or disaster at the primary site.However, the distance between the primary and secondary sites precludesusing a common disk resource for determining which node owns clusteroperations, if both the private and public Ethernet links fail.Consequently, if the servers in a cluster are separated by significantdistances, such as in a remote data mirroring system, and if both theprivate and public Ethernet links between the servers are notfunctioning, undesirable split brain operation can result because thereis no way for servers at one site to determine if servers at anothersite are operational.

SUMMARY

One aspect of the invention is a method for remotely monitoringactivity. An example of the method includes the operations of generatingfirst server heartbeat information at a first server at a local site,and storing the first server heartbeat information in a first primarysite disk at the local site. The method also includes sending the firstserver heartbeat information from the first primary site disk, to afirst secondary site disk at a remote site. The method further includesreceiving information from a second secondary site disk at the localsite, and determining if the information received from the secondsecondary site disk includes updated heartbeat information.

Other aspects of the invention are described in the sections below, andinclude, for example, a computing system, and a signal bearing mediumtangibly embodying a program of machine-readable instructions executableby a digital processing apparatus to perform a method for remotelymonitoring activity.

The invention provides a number of advantages. For example, theinvention advantageously permits servers at a local site that isseparated by a significant distance from servers at a remote site, todetermine if servers at the remote site are operational, even when bothprivate and public Ethernet links between the local and remote sites arenot functioning. Similarly, some examples of the invention also permitservers at the remote site to determine if servers at the local site areoperational. Consequently, undesirable split brain operation can beavoided. The invention also provides a number of other advantages andbenefits, which should be apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the hardware components andinterconnections of a geographically dispersed cluster in accordancewith an example of the invention.

FIG. 2 is an example of a signal-bearing medium in accordance an exampleof the invention.

FIG. 3 is a block diagram showing geographically dispersed site disks inaccordance with an example of the invention.

FIGS. 4A, 4B, and 4C are a flowchart of an operational sequence forremotely monitoring activity in accordance with an example of theinvention.

DETAILED DESCRIPTION

The nature, objectives, and advantages of the invention will become moreapparent to those skilled in the art after considering the followingdetailed description in connection with the accompanying drawings.

I. Hardware Components and Interconnections

One aspect of the invention is a computing system wherein serveractivity can be remotely monitored. As an example, the computing systemmay be embodied by the hardware components and interconnections ofgeographically dispersed cluster 100 shown in FIG. 1. The cluster 100may be used, for example, for processing and storing data for banks,governments, large retailers, or medical care providers.

The cluster 100 includes a first server 102 (which may also be called anode), and a first storage system 104, which are located at a local site106. The first server 102 is coupled to a first storage controller 108in the first storage system 104 with link 110, which may be, forexample, FCP (Fibre Channel Protocol) or parallel SCSI links. Similarly,the cluster 100 includes a second server 112, and a second storagesystem 114, which are located at a remote site 116. The second server112 is coupled to a second storage controller 118 in the second storagesystem 114 with link 120, which may be, for example, FCP or parallelSCSI links. The words “local” and “remote” are used to distinguishbetween two sites. However, the designation of one of the sites as“local” and the designation of the other site as “remote” is arbitrary.In other words, the “local” site could be referred to as the “remote”site, and the “remote” site could be referred to as the “local” site.Additionally, the second server 112 may be called the peer server (ornode) of the first server 102, and similarly, the first server 102 maybe called the peer server of the second server 112. As an example, thelocal site and the remote site may be separated by distances up to 103kilometers or more. The cluster 100 may be implemented, for example,utilizing Microsoft Cluster Service (MSCS), which is produced byMicrosoft Corporation, and the PPRC function of Enterprise StorageServers (ESS), which are manufactured by International Business MachinesCorporation.

In some examples of the cluster 100, the local site 106 could have morethan one server, and similarly, the remote site 116 could have more thanone server. Generally, any number of servers could be included at eachsite 106, 116, and in one example, four servers could be included ateach site 106, 116. In the example shown in FIG. 1, a third server 121,which would be coupled to other elements in the cluster 100 similarly tothe first server 102, is shown at the local site 106.

The first server 102 includes a first memory 122, a first non-volatilestorage 124, and a first processor 126. Similarly, the second server 112includes a second memory 128, a second non-volatile storage 130, and asecond processor 132. As an example, each of the processors 126, 132 maybe an Intel processor. In some examples, each server 102, 112 could havemore than one processor. The memories 122, 128 may be called fast accessstorage, and may be RAM. As an example, the memories 122, 128 may beused to store data and application programs and/or other programminginstructions executed by the processors 126, 132. The non-volatilestorage 124, 130 could be, for example, hard disk drives, or drives forreading and writing from optical or magneto-optical media, tape drives,or any other suitable type of storage. In some examples the memories122, 128 or the non-volatile storages 124, 130 could be eliminated, orthe memories 122, 128 and non-volatile storages 124, 130 could beprovided on the processors 126, 132, or alternatively, external from theservers 102, 112.

Each server 102, 112 may be, for example, an IBM xSeries server.Alternatively each server 102, 112 could be an IBM zSeries ParallelSysplex server, such as a zSeries 900, running the z Operating System(z/OS). In another example, each server 102, 112 could be an IBM S/390server running OS/390. Alternatively, each server 102, 112 could beimplemented with a mainframe computer, a computer workstation, apersonal computer, a supercomputer, or other suitable computing device.It is not necessary for each server 102, 112 to be implemented with thesame type of computing device.

The first storage system 104 includes a first quorum disk 134, one ormore first data disks 136, a first primary site disk 138, and a secondsecondary site disk 140, which are coupled to the first storagecontroller 108. Similarly, the second storage system 114 includes asecond quorum disk 142, one or more second data disks 144, a firstsecondary site disk 146, and a second primary site disk 148, which arecoupled to the second storage controller 118. Each disk 134, 136, 138,140, 142, 144, 146, 148 could also be implemented as a volume. In oneexample, the first storage system 104 and the second storage system 114are each a model 2105 Enterprise Storage Server, manufactured byInternational Business Machines Corporation. The first storagecontroller 108 may be coupled to the second storage controller 118 witha first ESCON link 150, and a second ESCON link 152, (which may beunidirectional, and which may also be called communications links orPPRC communications links). Appropriate communications technology otherthan ESCON could also be used for these links. When referring to thequorum disks 134, 142, data disks 136, 144, and site disks 138, 140,146, 148, the word “disk” is intended to broadly cover any suitable typeof storage device, using any suitable technology, such as magnetic,optical, magneto-optical, or electrical, and includes hard disk drives,optical disks or discs (for example, CD-RW, DVD−RW, or DVD+RW), floppydisks, magnetic data storage disks or diskettes, magnetic tape, digitaloptical tape, EPROMs, EEPROMs, RAM, Non-Volatile RAM, and flash memory.

The first server 102 is coupled to the second server 112 with a privatecommunications link 154, which may be a private Ethernet link. Clientcomputers 156, 158, 160, 162 are coupled to the first server 102 and thesecond server 112 via a public communications link 164, which providesanother or alternate communications path between the first server 102and the second server 112, and which may be a public Ethernet network.As an example, each client computer 156, 158, 160, 162 may be a personalcomputer, and may run any suitable operating system, for exampleWindows, Linux, Unix, or an Apple operating system. In someimplementations the public communications link 164, or the clientcomputers 156, 158, 160, 162 and the public communications link 164, maybe considered to be part of the cluster 100 rather than external to thecluster 100.

II. Operation

In addition to the hardware embodiments described above, another aspectof the invention concerns a method for remotely monitoring activity.

A. Signal-Bearing Media

In the context of FIG. 1, the method aspect of the invention may beimplemented, for example, by having one or more of the servers 102, 112execute a sequence of machine-readable instructions, which can also bereferred to as code. These instructions may reside in various types ofsignal-bearing media. In this respect, one aspect of the presentinvention concerns a programmed product, comprising a signal-bearingmedium or signal-bearing media tangibly embodying a program ofmachine-instructions executable by a digital processing apparatus toperform a method for remotely monitoring activity.

This signal-bearing medium may comprise, for example, first memory 122,first non-volatile storage 124, second memory 128, second non-volatilestorage 130, first data disks 136, and/or second data disks 144.Alternatively, the instructions may be embodied in a signal-bearingmedium such as the optical data storage disc 200 shown in FIG. 2. Theoptical disc can be any type of signal bearing disc or disk, forexample, a CD-ROM, CD-R, CD-RW, WORM, DVD−R, DVD+R, DVD−RW, or DVD+RW.Additionally, whether contained in the cluster 100 or elsewhere, theinstructions may be stored on any of a variety of machine-readable datastorage mediums or media, which may include, for example, a “harddrive”, a RAID array, a RAMAC, a magnetic data storage diskette (such asa floppy disk), magnetic tape, digital optical tape, RAM, ROM, EPROM,EEPROM, flash memory, magneto-optical storage, paper punch cards, or anyother suitable signal-bearing media including transmission media such asdigital and/or analog communications links, which may be electrical,optical, and/or wireless. As an example, the machine-readableinstructions may comprise software object code, compiled from a languagesuch as “C++”.

B. Overall Sequence of Operation

For ease of explanation, but without any intended limitation, the methodaspect of the invention is described with reference to the cluster 100described above and shown in FIG. 1. Additionally, FIG. 3, which is ablock diagram showing geographically dispersed site disks in accordancewith an example of the invention, may also facilitate understanding themethod aspect of the invention. FIG. 3 illustrates that a PPRC linkheartbeat from the first server 102 is stored on the first primary sitedisk 138 at the local site 106, and is transmitted across the PPRCcommunications link 150 to the first secondary site disk 146 at theremote site 116. Similarly, FIG. 3 illustrates that a PPRC linkheartbeat from the second server 112 is stored on the second primarysite disk 148 at the remote site 116, and is transmitted across the PPRCcommunications link 152 to the second secondary site disk 140 at thelocal site 106.

An example of the method aspect of the present invention is illustratedin FIGS. 4A, 4B, and 4C, which show a sequence 400 for a method forremotely monitoring activity. Referring to FIG. 4A, the sequence 400 mayinclude, and begin with, operation 402 which comprises establishingfirst and second PPRC pairs using a Read From Secondary option, whereinthe first PPRC pair comprises the first primary site disk 138 and thefirst secondary site disk 146, and the second PPRC pair comprises thesecond primary site disk 148 and the second secondary site disk 140. Insome examples of the invention, operation 400 comprises establishingonly the first PPRC pair or the second PPRC pair. PPRC usesunidirectional private communication links 150, 152 that may beimplemented using ESCON technology. Other examples of the invention maybe implemented with bidirectional communications link(s) rather thanunidirectional communication links. Using two of these links 150, 152,one in each direction, the PPRC pairs can be created, with the primaryof the first pair at a first site and the secondary of the first pair ata second site, and with the primary of the second pair at the secondsite and the secondary of the second pair at the first site.Establishing a PPRC pair may comprise making an initial copy of theinformation on the primary site disk, onto the secondary site disk, andthen entering a duplexed state wherein there is replication of allupdate activity.

The sequence 400 includes operation 404, which comprises generatingfirst server heartbeat information at the first server 102 at the localsite 106. Operation 406 comprises storing the first server heartbeatinformation in (or on) the first primary site disk 138 at the local site106. As an example, the first server heartbeat information may include atimestamp. More generally, the first server heartbeat information couldinclude a number from a sequence of incrementing or decrementingnumbers, and successive heartbeat information could include anothernumber from the sequence. The first server heartbeat information may begenerated by a PPRC Heartbeat Pumper thread, that periodically writes aunique timestamp to the first primary site disk 138, as long as the MSCScluster service is up and running. Each server 102, 112 may write to itsprimary site disk with a cluster-wide unique value(ClusterId+SystemTime) for each write. A pumping frequency that isapplicable to the entire cluster 100 may be given in the registry, whichmay be any configuration repository.

Operation 408 comprises sending (or attempting to copy) the first serverheartbeat information from the first primary site disk 138, to the firstsecondary site disk 146 at the remote site 116. As an example, thesending operation 408 may include reading the first server heartbeatinformation from the first primary site disk 138 and attempting totransmit the first server heartbeat information over the communicationslink 150 to the first secondary site disk 146 at the remote site 116. Ifreceived at the first secondary site disk 146, the first serverheartbeat information may be stored on the first secondary site disk146. Unless a pertinent portion of the cluster 100 is nonoperational,the sending operation 408 will be successful, and the first serverheartbeat information will be copied to the first secondary site disk146.

As an example, PPRC may be used to perform the sending operation 408.However, methods other than PPRC could be used for performing peer topeer remote copy. With PPRC, the first storage controller 108 at thelocal site 106 may forward the first server heartbeat information to thesecond storage controller 118 at the remote site 116. Also, with PPRC,the second storage controller 118 may notify the first storagecontroller 108 that the second storage controller 118 has received thefirst server heartbeat information, and then the first storagecontroller 108 may notify the first server 102 that storage of the firstserver heartbeat information has been completed.

The sequence 400 also includes operation 410, which comprises receivinginformation from the second secondary site disk 140, which may comprisereading from the second secondary site disk 140. The sequence 400 alsoincludes operation 412, which comprises determining if the informationreceived from the second secondary site disk 140 includes updatedheartbeat information (which may comprise determining if updatedheartbeat information has been stored on the second secondary site disk140). As an example, a separate thread or process in the first server102 may monitor the heartbeat(s) received from the remote site 116, anda separate thread or process in the second server 112 may monitor theheartbeat(s) received from the local site 106. A thread that monitors aheartbeat may be called a PPRC Heartbeat Monitor. The Heartbeat Monitormay be part of a PPRC Heartbeat thread that also includes the PPRCHeartbeat Pumper, or may be a separate thread. As an example, theHeartbeat Monitor checks the heartbeat received from the peer site, andexpects to see a different value each time it checks. Upon detecting aPPRC heartbeat miss, the Heartbeat Monitor may mark the peer site asbeing in the “NOTSURE” state. When the consecutive misses exceed acertain pre-defined threshold, the Heartbeat Monitor will announce thatthe peer is down. The receiving operation 410 and the determiningoperation 412 may be periodically repeated at a first frequency, and thegenerating 404, storing 406, and sending 408 operations may beperiodically repeated at a second frequency, that in some embodimentsmay be at least as large as the first frequency. Thus, a pollingtechnique is used to determine if the first server's 102 updatedheartbeat information has been received at the remote site 116. In someexamples, the operability of the PPRC links may be tested prior togenerating heartbeat information, or prior to sending heartbeatinformation to another site, or prior to determining if updatedheartbeat information has been stored.

Based on the receiving 410 and determining 412 operations, if it isdetermined that the information received from the second secondary sitedisk 140 includes updated heartbeat information, then the first server102 can conclude that updated heartbeat information has been receivedfrom the second server 112, and can conclude, in operation 414, that thesecond server 112 is operational, and that the PPRC data replication isalso operational. If in operation 412 it is determined that theinformation received from the second secondary site disk 140 does notinclude updated heartbeat information, then the sequence 400 may alsoinclude operation 416, which comprises determining if the PPRC state ofthe first primary site disk 138 is a suspended PPRC state. If it isdetermined that the PPRC state of the first primary site disk 138 is thesuspended PPRC state, then the sequence 400 may also include operation418, which comprises concluding that PPRC communications are notoperational, or that the second storage system 114 is not operational.If it is determined that the PPRC state of the first primary site disk138 is not the suspended PPRC state, then the sequence 400 may alsoinclude operation 420, which comprises concluding that the second server112 at the remote site 116 is not operational.

A confirmation signal indicating that the first server heartbeatinformation was received at the remote site 116, may be transmitted fromthe remote site 116 to the local site 106. The sequence 400 may alsoinclude operation 422, which comprises detecting whether a confirmationsignal is received at the local site 106 from the remote site 116. Ifthe confirmation signal is received at the local site 106, then inoperation 424 it may be concluded that the PPRC communications links150, 152 are operational, and that the second storage system 114 isoperational. If the confirmation signal is not received at the localsite 106 from the remote site 116, the state of the first primary sitedisk 138 at the local site 106 will become suspended. Further, if theconfirmation signal is not received at the local site 106 from theremote site 116, the sequence 400 may also include operation 426, whichcomprises determining whether communications between the first server102 and the second server 112 are operational over any communicationslink other than the PPRC communications links 150 and 152. For example,operation 426 may comprise determining whether communications betweenthe first server 102 and the second server 112 are operational over theprivate communications link 154, or the public communication link 164. Acondition where both the private communications link 154 (the firstlevel of arbitration) and the public communications link 164 (the secondlevel of arbitration) are not operational may be called a total networkcommunication fault. In situations where the PPRC communications links150 and 152 are operational, if a total network communication faultexists, then the quorum disk arbiter (also called the failover service)may use the site disks to determine if servers at peer location areoperational.

If in operation 426 it is determined that communications between thefirst server 102 and the second server 112 are operational over acommunications link such as communications link 154 and/or publiccommunication link 164, then the sequence 400 may also include operation428, which comprises implementing a fault mode. The choice of whichfault mode to implement may be user selectable in advance. An example ofa fault mode that may be implemented is a failstop fault mode, whichcomprises taking PPRC resources offline and shutting down MicrosoftCluster Service (MSCS) at the local site 106 and the remote site 116.This option may be used in environments where data integrity and dataconsistency are most important. An example of an alternative fault modethat may be implemented is a failover fault mode, which compriseskeeping a quorum owning server online, shutting down a peer server, andplacing all resources under control of the quorum owning server. Thisoption may be used in environments where data availability is mostimportant. An example of another alternative fault mode that may beimplemented is a No_New_Onlines fault mode, which comprises keeping aquorum owning server online and having resources stay online, shuttingdown cluster service at a peer server, and taking all of the peerserver's resources offline. The No_New_Onlines fault mode may be thedefault option. An example of another alternative fault mode that may beimplemented is an Online_No_Moves fault mode, which comprises keepingthe first server 102 and the second server 112 online, and not takingany resources offline, and not allowing disk failover between the sitesuntil the PPRC link is active and the disks are synchronized.

Referring to FIG. 4B, the sequence 400 may also include operation 434,which comprises generating second server heartbeat information at thesecond server 112 at the remote site 116, and may also include storingthe second server heartbeat information in the second primary site disk148 at the remote site 116, in operation 436. As an example, the secondserver heartbeat information may include a timestamp. The sequence 400may also include operation 438, which comprises sending (which maycomprise attempting to copy) the second server heartbeat informationfrom the second primary site disk 148, to the second secondary site disk140 at the local site 106. As an example, the sending operation 438 mayinclude reading the second server heartbeat information from the secondprimary site disk 148 and attempting to transmit the second serverheartbeat information over the communications link 152. Unless apertinent portion of the cluster is nonoperational, the sendingoperation 438 will be successful, and the second server heartbeatinformation will be copied to the second secondary site disk 140. As anexample, PPRC may be used to perform the copying operation 418. Thesequence 400 may also include operation 440, which comprises receivinginformation from the first secondary site disk 146, which may comprisereading from the first secondary site disk 146. The sequence 400 mayalso include operation 442, which comprises determining if theinformation received from the first secondary site disk 146 includesupdated heartbeat information (which may comprise determining if updatedheartbeat information has been stored on the first secondary site disk146). The receiving operation 440 and the determining operation 442 maybe periodically repeated at a first frequency, and the generating 404,storing 406, and sending 408 operations (discussed above with referenceto FIG. 4A) may be periodically repeated at a second frequency that maybe at least as large as the first frequency.

Based on the receiving 440 and determining 442 operations, if itdetermined that the information received from the first secondary sitedisk 146 includes updated heartbeat information, then the second server112 can conclude that updated heartbeat information has been receivedfrom the first server 102, and can conclude, in operation 444, that thefirst server 102 is operational, and that the PPRC data replication isalso operational. If in operation 442 it is determined that theinformation received from first secondary site disk 146 does not includeupdated heartbeat information, then the sequence 400 may also includeoperation 446, which comprises determining if the PPRC state of thesecond primary site disk 148 is a suspended PPRC state. If it isdetermined that the PPRC state of the second primary site disk 148 issuspended, then in operation 448 it is concluded that PPRCcommunications are not operational, or that the first storage system 104is not operational. If it is determined that the PPRC state of thesecond primary site disk 148 is not the suspended PPRC state, then thesequence 400 may also include operation 450, which comprises concludingthat the first server 102 at the local site 106 is not operational.

A confirmation signal indicating that the second server heartbeatinformation was received at the local site 106, may be transmitted fromthe local site 106 to the remote site 116. The sequence 400 may alsoinclude operation 452, which comprises detecting whether a confirmationsignal is received at the remote site 116 from the local site 106. Ifthe confirmation signal is received at the remote site 116, then inoperation 454 it may be concluded that the PPRC communications links150, 152 are operational, and that the first storage system 104 isoperational. If the confirmation signal is not received at the remotesite 116 from the local site 106, the state of the second primary sitedisk 148 at the remote site 116 will become suspended. Further, if theconfirmation signal is not received at the remote site 116 from thelocal site 106, the sequence 400 may also include operation 456, whichcomprises determining whether communications between the first server102 and the second server 112 are operational over any communicationslink other than the PPRC communications links 150 and 152. For example,operation 456 may comprise determininng whether communications betweenthe first server 102 and the second server 112 are operational over theprivate communications link 154, or the public communication link 164.

If in operation 456 it is determined that communications between thefirst server 102 and the second server 112 are operational over acommunications link such as the private communications link 154 and/orpublic communication link 164, then the sequence 400 may also includeoperation 458, which comprises implementing a fault mode, as discussedabove.

In a first example, each server 102, 121 at the local site 106 maygenerate heartbeat information, which may be stored on the first primarysite disk 138 (or on more than one site disk), and copied from the firstprimary site disk 138 to the first secondary site disk 146. In a secondexample, if there is more than one server at the local site 106,whichever server is in control of the cluster at the local site 106could generate heartbeat information for the local site 106, which inthis second example, would be the only heartbeat information from thelocal site 106. In the second example, if the first server 102 becomesnonoperational, the third server 121 could generate heartbeatinformation for the local site 106.

FIG. 4C shows operations for an example of the invention in which thethird server 121 (shown in FIG. 1) is included at the local site 106,and in which the third server 121 generates third server heartbeatinformation. As shown in FIG. 4C, the sequence 400 may include operation464, which comprises generating third server heartbeat information atthe third server 121 at the local site 106, and operation 466, whichcomprises storing the third server heartbeat information in the firstprimary site disk 138 at the local site 106. The sequence 400 may alsoinclude sending the third server heartbeat information from the firstprimary site disk 138 to the first secondary site disk 146 at the remotesite 116, in operation 468. The sequence 400 also includes operation470, which comprises receiving information from the second secondarysite disk 140, which may comprise reading from the second secondary sitedisk 140. The sequence 400 also includes operation 472, which comprisesdetermining if the information received from the second secondary sitedisk 140 includes updated heartbeat information (which may comprisedetermining if updated heartbeat information has been stored on thesecond secondary site disk 140). The receiving operation 470 and thedetermining operation 472 may be periodically repeated at a firstfrequency, and the generating 464, storing 466, and attempting to copy468 operations may be periodically repeated at a second frequency thatin some embodiments may be at least as large as the first frequency.

Based on the receiving 470 and determining 472 operations, if it isdetermined that the information received from the second secondary sitedisk 140 includes updated heartbeat information, then the third server121 can conclude that updated heartbeat information has been receivedfrom the second server 112, and can conclude, in operation 474, that thesecond server 112 is operational, and that the PPRC data replication isalso operational. If in operation 472 it is determined that theinformation received from the second secondary site disk 140 does notinclude updated heartbeat information, then the sequence 400 may alsoinclude operation 476, which comprises determining if the PPRC state ofthe first primary site disk 138 is a suspended PPRC state. If it isdetermined that the PPRC state of the first primary site disk 138 is thesuspended PPRC state, then the sequence 400 may also include operation478, which comprises concluding that PPRC communications are notoperational, or that the second storage system 114 is not operational.If it is determined that the PPRC state of the first primary site disk138 is not the suspended PPRC state, then the sequence 400 may alsoinclude operation 480, which comprises concluding that the second server112 at the remote site 116 is not operational.

A confirmation signal indicating that the third server heartbeatinformation was received at the remote site 116, may be transmitted fromthe remote site 116 to the local site 106. The sequence 400 may alsoinclude operation 482, which comprises detecting whether a confirmationsignal is received at the local site 106 from the remote site 116. Ifthe confirmation signal is received at the local site 106, then inoperation 484 it may be concluded that the PPRC communications links150, 152 are operational, and that the second storage system 114 isoperational. If the confirmation signal is not received at the localsite 106 from the remote site 116, the state of the first primary sitedisk 138 at the local site 106 will become suspended. Further, if theconfirmation signal is not received at the local site 106 from theremote site 116, the sequence 400 may also include operation 486, whichcomprises determining whether communications between the third server121 and the second server 112 are operational over any communicationslink other than the PPRC communications links 150 and 152. For example,operation 486 may comprise determining whether communications betweenthe third server 121 and the second server 112 are operational over theprivate communications link 154, or the public communication link 164.

If in operation 486 it is determined that communications between thethird server 121 and the second server 112 are operational over acommunications link such as communications link 154 and/or publiccommunication link 164, then the sequence 400 may also include operation488, which comprises implementing a fault mode, as discussed above.

When a server fails, the server that owns the quorum resource may bringthe resources owned by the faulted server online on the next server ineach failover group's preferred owner list. In the case where the serverthat owns the quorum resource fails, the remaining servers may arbitratefor the quorum resource, and then bring the resources from the failedserver online on the next server in each failover group's preferredowner list. Each failover group has a priority based ordered list ofservers that are capable of bringing all resources in the failover grouponline. In the case of a failover, the next highest server in the listis chosen to bring the failover group online.

The site disk PPRC pairs use the PPRC feature Read From Secondary (RFS),which provides read only access, to allow a server that has access toone of the secondary site disks 140, 146 to read the heartbeatinformation on disk that is being updated by a server (or servers) atthe other site. If the heartbeat information is being updated, then theserver(s) at the other site that are updating the heartbeat informationare known to be operational (and it is also known that PPRC is activeand that the storage subsystem at the other site is operational). If theheartbeat information is not being updated then one of two situationshas occurred: (1) the link, or the storage (sub)system at the other siteare down, or, (2) the server(s) at the other site are not operational.To determine which situation has occurred, the PPRC state of the primarysite disk is checked at the site that is not receiving updated heartbeatinformation. PPRC states can be (1) active (duplexed), which is in thenormal operational state, (2) suspended, because there is either acommunication fault or a problem with the target storage subsystem, or(3) not active, because a PPRC pair has been terminated.

If the PPRC state of a primary site disk is suspended, the suspendedcondition is the result of either the PPRC link being down or thestorage system at the other site being down. If a storage system isdown, IsAlive will fail on all servers at the site of the failed storagesystem. The IsAlive function is used for a thorough resource statusevaluation and is regularly polled by the Resource Monitor. If the PPRCstate of a primary site disk 140, 146 is not suspended, then it can beconcluded that the PPRC link is operational (active), and that thestorage system at the other site is operational. Additionally, if thePPRC state of a primary site disk at a site is not suspended, butupdated heartbeat information is not being received from another site,then it can be concluded that the server(s) are not operational at thesite from which the heartbeat signals are not being received. A “cleanending status” is achieved if after heartbeat information is writtenfrom a server to a primary site disk and is copied to a secondary sitedisk at another site, a confirming signal is received at the site of theprimary site disk from the site of the secondary site disk. Theconfirming signal indicates that the heartbeat information was receivedat the secondary site disk.

The invention facilitates transferring the state (active or not active)of a first server connected to a (PPRC) primary site disk (or volume) atone site, to a corresponding secondary site disk (or volume) at anothersite. The site disks typically are used for management purposes only,and are not used as data disks. A second server at the site of the(PPRC) secondary volume can then access the state of the server locatedat the site of the primary site disk by reading the state informationfrom the (PPRC) secondary volume. This is possible because the PPRC pairis established using the Read From Secondary option. A different PPRCpair established in the opposite direction permits transferring thesecond server's state to the first server. Alternatively, bidirectionalcommunication link(s) could be used. In one alternative example, abidirectional communication link could be used, and server heartbeatscould be stored on different areas of a single site disk at each site.Irrespective of whether unidirectional or bidirectional communicationlinks are used, this technique permits a server at a site in ageographically dispersed cluster that is using outboard mirroring (suchas PPRC), to determine the state of the servers at a different site,even when other cluster heartbeat communication link(s), such as theprivate communications link 154 and the public communications link 164,are not operational. Thus, in situations where a common resource such asa quorum disk or arbitration server cannot be used as the third level ofarbitration for ownership of the cluster, for example in ageographically dispersed cluster, the method of the invention can beused to provide the third level of arbitration. The first level ofarbitration is provided by a private communication link such as link154, and the second level of arbitration is provided by a publiccommunications link such as link 164. The invention provides the thirdlevel of arbitration by using PPRC communications to allow server(s) todetermine if server(s) at another site in a cluster are stilloperational. In other words, the invention utilizes PPRC to provide acommon resource that can be used as a third level of arbitration insteadof a quorum disk or arbitration server. Thus, use of the invention canbeneficially prevent the split brain syndrome for both majority-node-setclusters and shared-quorum clusters in geographically dispersedconfigurations.

III. Other Embodiments

While the foregoing disclosure shows a number of illustrativeembodiments of the invention, it will be apparent to those skilled inthe art that various changes and modifications can be made hereinwithout departing from the scope of the invention as defined by theappended claims. Furthermore, although elements of the invention may bedescribed or claimed in the singular, the plural is contemplated unlesslimitation to the singular is explicitly stated.

1. A method for remotely monitoring activity, the method comprising thefollowing operations: generating first server heartbeat information at afirst server at a local site; storing the first server heartbeatinformation on a first primary site disk at the local site; periodicallyrepeating at a second frequency, the operation of sending the firstserver heartbeat information from the first primary site disk, to afirst secondary site disk at a remote site; periodically repeating at afirst frequency, wherein the second frequency is larger than the firstfrequency, the operation of receiving information from a secondsecondary site disk at the local site; determining if the informationreceived from the second secondary site disk includes updated heartbeatinformation, and if so, transmitting a confirming signal from the localsite to the remote site, wherein the confirming signal transmitted fromthe local site indicates that updated heartbeat information was receivedfrom the remote site at the local site; and determining if theinformation received from the second secondary site disk at the localsite does not include updated heartbeat information for a pre-definedthreshold consecutive number of repetitions of the operation ofreceiving information from the second secondary site disk at the localsite.
 2. The method of claim 1, wherein the method further comprises thefollowing operations: detecting whether the confirming signal isreceived at the remote site; generating second server heartbeatinformation at a second server at the remote site; storing the secondserver heartbeat information on a second primary site disk at the remotesite; sending the second server heartbeat information from the secondprimary site disk, to a second secondary site disk at the local site;receiving information from the first secondary site disk at the remotesite; determining if the information received from the first secondarysite disk includes updated heartbeat information, and if so,transmitting a confirming signal from the remote site to the local site,wherein the confirming signal transmitted from the remote site indicatesthat updated heartbeat information was received from the local site atthe remote site; and determining if the information received from thefirst secondary site disk does not include updated heartbeat informationfor a pre-defined threshold consecutive number of repetitions of theoperation of receiving information from the first secondary site disk atthe remote site.
 3. The method of claim 2, wherein the method furthercomprises the operation of establishing first and second PPRC pairsusing a Read From Secondary option, wherein the first PPRC paircomprises the first primary site disk and the first secondary site disk,and the second PPRC pair comprises the second primary site disk and thesecond secondary site disk.
 4. The method of claim 1, wherein the methodfurther comprises the operation of establishing a PPRC pair using a ReadFrom Secondary option, wherein the PPRC pair comprises the first primarysite disk and the first secondary site disk.
 5. The method of claim 1,wherein PPRC is used to perform the sending operation.
 6. The method ofclaim 1, wherein the sending operation comprises: receiving the firstserver heartbeat information from the first primary site disk; andattempting to transmit the first server heartbeat information over acommunications link to the remote site.
 7. The method of claim 1,wherein the first server heartbeat information comprises a timestamp. 8.The method of claim 1, wherein the method further comprises thefollowing operations: generating third server heartbeat information at athird server at the local site; storing the third server heartbeatinformation in the first primary site disk at the local site; andsending the third server heartbeat information from the first primarysite disk, to the first secondary site disk at the remote site.
 9. Amethod for remotely monitoring activity, the method comprising thefollowing operations: generating first server heartbeat information at afirst server at a local site; storing the first server heartbeatinformation on a first primary site disk at the local site; periodicallyrepeating at a second frequency, the operation of sending the firstserver heartbeat information from the first primary site disk, to afirst secondary site disk at a remote site; periodically repeating at afirst frequency, wherein the second frequency is larger than the firstfrequency, the operation of receiving information from a secondsecondary site disk at the local site; determining if the informationreceived from the second secondary site disk includes updated heartbeatinformation, and if so, transmitting a confirming signal from the localsite to the remote site, wherein the confirming signal transmitted fromthe local site indicates that updated heartbeat information was receivedfrom the remote site at the local site; determining if the informationreceived from the second secondary site disk at the local site does notinclude updated heartbeat information for a pre-defined thresholdconsecutive number of repetitions of the operation of receivinginformation from the second secondary site disk at the local site;detecting whether the confirming signal is received at the remote site;generating second server heartbeat information at a second server at theremote site; storing the second server heartbeat information on a secondprimary site disk at the remote site; sending the second serverheartbeat information from the second primary site disk, to a secondsecondary site disk at the local site; receiving information from thefirst secondary site disk at the remote site; determining if theinformation received from the first secondary site disk includes updatedheartbeat information, and if so, transmitting a confirming signal fromthe remote site to the local site, wherein the confirming signaltransmitted from the remote site indicates that updated heartbeatinformation was received from the local site at the remote site; anddetermining if the information received from the first secondary sitedisk does not include updated heartbeat information for a pre-definedthreshold consecutive number of repetitions of the operation ofreceiving information from the first secondary site disk at the remotesite.
 10. The method of claim 9, wherein PPRC is used to perform thesending operations.